The present invention generally relates to a rotary printing machine and, more particularly, to an ink detecting device for use in the rotary printing machine for detecting the quantity of a printing ink supplied onto an outer periphery of printing drum.
There is known a rotary printing machine of a type wherein, during the rotation of the printing drum, a printing ink supplied onto the outer periphery of the printing drum is allowed to penetrate through the image area of the stencil to a paper positioned on one side of the stencil opposite to the drum and being moved in same direction in synchronism with the rotation of the drum. With this known rotary printing machine, the printing ink has to be replenished with a predetermined quantity upon a time predetermined number of papers have been printed, or the printing ink has to be manually replenished occasionally depending on the tone or the quality of the printed image on the papers being monitored by the attendant operator. The replenishment of the printing ink against the predetermined number of the papers printed or the manual replenishment of the printing ink against the tone or the quality of the printed image on the paper is disadvantageous not only in that the image can not be uniformly printed on all of the papers, but also in that it is a time-consuming and tiresome procedure.
In view of the above, an ink detecting device for detecting the quantity of ink remaining on the outer periphery of the printing drum has been devised and disclosed in, for example, the first Japanese Patent Publication No. 58-74361, published on May 4, 1983. According to this publication, the ink detecting device comprises a plurality of sensor rolls, each of which is so fixedly mounted on a corresponding shaft, rotatably supported by a machine framework, as to be in frictional contact with a corresponding portion of an outer periphery of an applicator roll and also as to be moved together with the shaft in one axial direction thereof due to the ink layer on the applicator roll during the operation of the printing machine, the shifted length of each sensor roll being proportional to the thickness of the ink layer. The printing ink is controlled to be replenished from an ink supplying device onto a corresponding portion of outer peripheral surface of the printing drum when the shifted length of each sensor roll falls below a predetermined reference value.
Meanwhile, it is well known that the more the temperature of the printing ink is low, the more the viscosity thereof become high so that, when the temperature of the printing ink is lower than normal, the printing ink is required to be replenished on the printing drum much more than normal. In such case, however, with this known ink detecting device, since the thickness of the printing ink with viscosity higher than normal is generally regarded to be larger than normal dimension, namely, since it is regarded that the sufficient quantity of the printing ink remains on the corresponding portion of the printing drum, it disadvantageously results in that the printing ink can not be replenished onto the printing drum sometimes although it should be replenished. While, according to above prior art, when the temperature of the printing ink is higher than the normal one, since the viscosity of the printing ink is lower than normal, the printing ink is disadvantageously possibly replenished too much onto the printing drum.